The present invention relates to a coupling device to attach a trailer or any other towable implement to a tractor. The device includes a drawbar mounted under the tail section of the tractor. The drawbar is lowerable, downwardly, out of its towing position and has a coupling member on its rearwardly projecting end.
A known coupling device is illustrated by GB-A-1225761. Here, a drawbar has a coupling member supported laterally by connecting pins. Tiltable framework supports the drawbar, however, the laterally rigid attachment of the drawbar relative to the framework makes coupling difficult.
An object of the present invention is to provide a coupling device which facilitates coupling of a towable implement or trailer to a tractor.
In accordance with one aspect of the invention, a coupling device is mountable on a tractor to releasably connect a towable member to the tractor. The device includes a drawbar movable, in use, relative to the tractor, on which the coupling device is mounted, between a lower inoperative position in which the towable member is connectable to and disconnectable from the drawbar and an upper operative position in which the towable member is towable by the tractor. The device further includes a centering means with abutment members. When the drawbar is in its upper operative position, the abutment members are engageable in contact with one another to center the drawbar relative to the device. When the drawbar is in its lower inoperative position, the abutment members are disengaged from contact with one another.
An advantage of the arrangement described in the preceding paragraph is that it is possible to adjust the drawbar laterally in order to attach a towable implement or trailer to the tractor. Thus, the operator need not perform any further manual operation to release the drawbar in a lateral direction other than the normal lowering operation of the drawbar.
The invention proposes that by raising the drawbar, the abutment members, with the centering means, are brought into engagement with one another thus effecting the desired alignment. The raising movement transfers the drawbar into its aligned position. Also, it is possible for the abutment members, with the centering means, to be brought into engagement with one another through a separate power drive associated with the drawbar. In such an embodiment, the lifting movement to bring the drawbar into its raised towing position and the movement of the drawbar into its centered position occur separately from one another. Such movements may however take place simultaneously.
In one embodiment of the invention, the drawbar is supported on a framework. The drawbar has one or more centering faces for lateral alignment in relation to the framework. When the framework, mounted on the rear underside of the tractor, is lowered the centering faces are brought out of engagement with butting faces on the framework. When the drawbar is raised to the towing position, the faces are brought into engagement. Thus, when the towing position is adopted the drawbar is in alignment. Also, the centering faces may be on separate centering pieces which are detachably secured to the drawbar.
The centering means can alternatively include attachments fixed to the underside of the tractor. In such an arrangement, the drawbar is provided with one or more lateral alignment centering faces. The centering means is fixed on the rear underside of the tractor laterally aligning the drawbar when it is in its towing position. The drawbar can be supported on framework which is secured on the rear underside of the tractor in such a manner that it can be raised and lowered relative to the tractor.
In order to be able to alter the position of the coupling member, the drawbar is mounted on slide means. The slide means is guided so that it can move axially on the framework. Thus, the drawbar can rotate about a vertical axis.
Various means can be employed for mounting the framework to the rear underside of the tractor. If the coupling member is to remain at about the same distance from the rear of the tractor during lowering and raising of the drawbar, the framework may be connected to the underside of the rear of the tractor at the end remote from the implement to be towed so that the framework may pivot about a horizontal axis. If the coupling member is to be extended to any great degree towards the to be attached implement, the framework is connected to the rear underside of the tractor by varying length links.
The slide means is preferably force-guided so that, in a simple mechanical manner, the position of the coupling member relative to the rear of the tractor remains largely constant during the raising and lowering operation. Thus, the direction of the longitudinal axis of the tractor is not altered relative to the coupling member. In order to achieve the forced movement of the slide means, it is connected, via links, to a swivel bearing which is fixed in relation to the tractor.
In order to achieve a constant position of the coupling member in relation to the rear of the tractor, in the case of a swivel bearing, the swivel bearing is positioned closer to the rearward projecting coupling member than the linkage point of the links on the slide means to the coupling member. In the case of a bearing block, the bearing carrying the framework is offset forward from the linkage point of the links on the slide means in the direction of the longitudinal axis of the tractor.
In order to facilitate centering and guidance of the drawbar into its locked position, i.e. its laterally immovable position in the towing position, the centering faces of the drawbar, in a direction starting from the towing position in which they are supported laterally between the butting faces, are designed to converge towards the front in the direction of the longitudinal axis of the tractor. The guide cross-section of the centering pieces thus becomes smaller and allows lateral play towards the stop blocks and therefore a slow convergence during the coupling operation.
To lock the framework in the upper towing position, it is further proposed to provide a locking mechanism which secures the framework in relation to the tractor.
The drawbar can be fitted at each of its ends with differing coupling members to accommodate various types of towable members. The coupling members are circumferentially offset in relation to one another about the longitudinal axis of the drawbar. The coupling members in the towing position have a cross-section which is smaller than the opening cross-section of the framework in the region of the stop blocks. Thus, it is possible by simply removing the drawbar and changing the centering pieces to attach another type of attachment. Also, extension fins may be on the centering pieces in order to facilitate coupling and aligning of the drawbar in a lateral direction in relation to coupling members associated with the to be attached implement or trailer.
Instead of the forced guidance of the slide means via links it may be possible to move the slide means by a power drive. In this case, the raising and lowering movement of the drawbar may be effected separately from its displacement.
In the case of a fixed centering means, the centering means, in a first alternative, includes a swivelling centering lever which rests on the centering faces of the drawbar. Alternatively, the fixed centering device may include a centering fork secured to the rear underside of the tractor. The fork has a supporting recess for the drawbar which opens into obliquely extending faces.
Furthermore, the framework is able to be lifted and lowered by means of a power drive engaged with the framework. Such a power drive can be the lifting drive of the tractor, which is provided for the conventional lower guide linkage, or a separate lifting device may be provided, for example a piston and cylinder unit may be provided on the framework.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.